Reactions of diarsines with bi- And tri-metallic carbonyl complexes containing cobalt

Article abstract of DOI:10.1039/a906611j

Reaction of the diarsines As₂R₄ (R = Me or Ph) with alkyne-bridged dicobalt hexacarbonyl complexes leads to products with bridging (AsR₂)₂O ligands and to the production of simple AsR₃ substituted complexes; alkylidyne tricobalt nonacarbonyl complexes exhibit parallel reactivity with As₂R₄. Thermolysis of the complex [Co₂(μ-PhCCPh){μ-(AsMe₂)₂O}(CO) ₄] gives the tetra-substituted complex, [Co₂(μ-PhCCPh){μ-(AsMe₂)₂O} ₂(CO)₂]. Reaction of the heterometallic complex [(OC)₃Co{μ-C₂(CO₂Me) ₂}MoCp(CO)₂] with As₂Ph₄ affords [{(HO)Ph₂As}-(OC)₂Co{μ-C₂(CO ₂Me)₂}MoCp(CO)₂], supporting the suggestion of a possible hydrolytic mechanism for the formation of the (AsR₂)₂O bridged complexes. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/a906611j

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Reactions of diarsines with bi- and tri-metallic carbonyl complexes
containing cobalt
Nick Choi,a Gráinne Conole,a Jason D. King,†b Martin J. Mays,*b Mary McPartlina
and Caroline L. Stoneb
a School of Applied Chemistry, University of North London, Holloway Road, London,
UK N7 8DB
b Department of Chemistry, Lensfield Road, Cambridge, UK CB2 1EW
Received 16th August 1999, Accepted 25th November 1999
Reaction of the diarsines As2R4 (R = Me or Ph) with alkyne-bridged dicobalt hexacarbonyl complexes leads
to products with bridging (AsR2)2O ligands and to the production of simple AsR3 substituted complexes;
alkylidyne tricobalt nonacarbonyl complexes exhibit parallel reactivity with As2R4. Thermolysis of the complex
[Co2(µ-PhCCPh){µ-(AsMe2)2O}(CO)4] gives the tetra-substituted complex, [Co2(µ-PhCCPh){µ-(AsMe2)2O}2(CO)2].
Reaction of the heterometallic complex [(OC)3Co{µ-C2(CO2Me)2}MoCp(CO)2] with As2Ph4 affords [{(HO)Ph2As}-
(OC)2Co{µ-C2(CO2Me)2}MoCp(CO)2], supporting the suggestion of a possible hydrolytic mechanism for the
formation of the (AsR2)2O bridged complexes.
In this paper we report the reactions of the diarsine ligands
Introduction
As2R4 (R = Me or Ph) with some bi- and tri-metallic carbonyl
complexes containing cobalt and compare them with the reac-
tions of their P2R4 analogues.
Thermally induced cleavage of the E–E bond of E2R4 (E = P,
As) in the presence of metal carbonyls has proved a useful route
to bis-ER2-bridged bimetallic complexes.1 Under milder con-
ditions, complexes have also been synthesised which contain
intact E2R4 ligands;1,2 most examples of intact E2R4 ligands are
for E = P, the number of characterised diarsine complexes being
fairly small.3 The diarsine in such complexes is often generated
during the course of the reaction rather than being used as a
starting material.
More recently, the reaction of P2Ph4 with the alkyne-bridged
dicobalt complexes, [Co2(µ-RCCRЈ)(CO)6] [R = RЈ = CO2Me,
Ph or H; R = Ph, Me or CH2OH, RЈ = H], has been investigated
under mild conditions.4 Carbonyl substitution occurs readily
to give derivatives in which an intact P2Ph4 molecule is coordin-
ated in either a terminal monodentate or bridging bidentate
mode. Cleavage of the P–P bond also occurs readily to produce
complexes with four- or five-membered phosphametalla-
cycles, via a proposed intermediate that possesses two PPh2
groups, one terminal and one bridging.4 The related mixed-
metal complexes [(OC)3Co(µ-RCCRЈ)MoCp(CO)2] [R = RЈ =
CO2Me; R = Ph, RЈ = H] react with P2Ph4 to give products that
feature four-membered phosphacobaltacycles (Co–C–C–P);
mono-substituted derivatives of the alkyne-bridged starting
complex have also been isolated, in which the diphosphine is
coordinated intact in monodentate mode.5
Results and discussion
(i) Synthesis and spectroscopy
(a) Reaction of [Co2(ꢀ-RCCRЈ)(CO)6] (R ؍ RЈ ؍ Ph;
R ؍ Ph, RЈ ؍ H; R ؍ Me, RЈ ؍ H) with As2Ph4. Reaction of
[Co2(µ-RCCRЈ)(CO)6] (R = RЈ = Ph; R = Ph, RЈ = H; R = Me,
RЈ = H) with one equivalent of As2Ph4 in toluene at 40 ЊC
gave, in addition to unreacted starting materials, green [Co2-
(µ-RCCRЈ)(CO)5(AsPh3)] [R = RЈ = Ph (1a) (4%) or R = Ph,
RЈ = H (1b) (20%)] and purple [Co2(µ-RCCRЈ){µ-(AsPh2)2O}-
(CO)4] [R = RЈ = Ph (2a) (60%); R = Ph, RЈ = H (2b) (10%);
R = Me, RЈ = H (2c) (43%)]. Proposed structures for the
products are shown in Fig. 1. All the complexes have been
characterised by IR spectroscopy, mass spectrometry and
microanalysis. 1H and 13C NMR data have been collected
for complexes 1b, 2a, 2b and 2c. In addition, X-ray diffraction
studies have established the molecular structure shown in
Fig. 2(a) for 2b.
1
The H NMR spectra of 2a–2c exhibit phenyl resonances.
For complex 2a, no other signals are observed. For 2b a further
1
singlet at δ 5.75 is ascribed to the acetylenic proton. The H
NMR spectrum of 2c shows two singlets in addition to the
phenyl resonances. A signal at δ 5.47 corresponding to one
proton is assigned to the acetylenic hydrogen atom, while a
further peak at δ 2.68 with three-times the intensity of the first
is attributed to the acetylenic methyl group.
Reaction of the µ3-alkylidyne tricobalt nonacarbonyl com-
plexes [Co3(µ3-CR)(CO)9], with P2Ph4 initially proceeds to give
complexes that contain the intact diphosphine in a terminal or
bridging coordination mode.6 Cleavage of the P–P bond again
seems the most likely next step, but in this case metallacycle
formation does not ensue. Instead, on chromatographic
separation of the reaction mixture, a complex containing a
µ-[(PPh2)2O] ligand is isolated. For this reaction the inter-
mediacy of a bis-phosphido bridged complex followed by
hydrolysis/oxidation (on silica) of the intermediate has been
proposed and this proposal is able to account for the generation
of the products that feature the µ-[(PPh2)2O] ligand.6
The 13C spectrum of 2a exhibits a broad peak at δ 203.1 due
to the carbonyl groups in addition to phenyl resonances. There
are two peaks for the ipso-carbons of the phenyl groups,
indicating that these occur in two distinct environments.
One group of phenyl signals can be attributed to the acetyl-
enic phenyl rings, the other to the phenyl groups in the
(AsPh2)2O ligand. The fact that the four phenyl groups of the
bridging ligand are all equivalent must be attributable to a
fluxional process, the nature of which is discussed for complex
2c below.
† Present address: Department of Chemistry, The University of Mon-
tana, Missoula, 59812 Montana, USA.
J. Chem. Soc., Dalton Trans., 2000, 395–405
This journal is © The Royal Society of Chemistry 2000
395

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Fig. 2 (a) Molecular structure of [Co2(µ-PhCCH){µ-AsPh2)2O}(CO)4]
(2b) and (b) molecular structure of [Co2{µ-C2(CO2Me)2}{µ-(AsMe2)2-
O}(CO)4] (4c) including atom numbering scheme.
Fig. 1 Proposed structures of the new complexes.
has been observed previously for the analogous µ-P2Ph4 com-
plexes [Co2(µ-RCCRЈ)(µ-P2Ph4)(CO)4].4
The 13C NMR spectrum of 2c includes resonances due to
carbonyl and phenyl carbon atoms, singlets at δ 103.4 and δ 73.6
attributable to the acetylenic CMe and CH carbons respectively
and a signal at δ 22.5, which is assigned to the carbon atom of
the acetylenic methyl group. There are two ipso-carbon signals
indicating two environments for the phenyl groups of the
(AsPh2)2O ligand.
If 2c adopts in solution the structure found for 2b in the
solid state [Fig. 2(a)], in which the bridging (AsPh2)2O ligand
occupies equatorial sites on each of the cobalt atoms, then in
principle two isomers are possible. In one, the equatorial sites
occupied will be closest to the methyl substituent on the alkyne
ligand, and in the other they will be closest to the H substituent.
Two phenyl resonances are expected for the non-equivalent
phenyl groups in each isomer and, accordingly, if both isomers
are present in solution, four ipso-carbon resonances should be
observed. The fact that only two resonances are observed
implies either that only one isomer is present in solution or that
a fluxional process is operative resulting in isomer intercon-
version which is fast on the NMR timescale. Such a fluxional
process must be operative for 2a to account for the observations
of only one environment for the phenyl groups, and it therefore
seems likely to be operative for 2c as well. Similar fluxionality
(b) Reaction of [Co2(ꢀ-RCCRЈ)(CO)6] [R ؍ RЈ ؍ Ph;
R ؍ Ph, RЈ ؍ H; R ؍ RЈ ؍ CO2Me] with As2Me4. Reaction of
[Co2(µ-RCCRЈ)(CO)6] [R = RЈ = Ph; R = Ph, RЈ = H; R =
RЈ = CO2Me] with one equivalent of As2Me4 in toluene at 40 ЊC
gave, in addition to unreacted starting materials, the monosub-
stituted trimethyl arsine complexes [Co2(µ-RCCRЈ)(CO)5-
(AsMe3)] [R = RЈ = Ph (3a) (12%); R = Ph, RЈ = H (3b) (17%),
R = RЈ = CO2Me (3c) (25%)] and the (AsMe2)2O bridged com-
plexes [Co2(µ-RCCRЈ){µ-(AsMe2)2O}(CO)4] [R = RЈ = Ph (4a)
(21%); R = Ph, RЈ = H (4b) (18%); R = RЈ = CO2Me (4c)
(35%)]. Proposed structures for the products are shown in
Fig. 1. All complexes have been characterised by IR, 1H and 13
C
NMR spectroscopy and mass spectroscopy. Microanalytical
data have been obtained for all complexes with the exception of
3b. A single crystal X-ray diffraction study of complex 4c shows
it to have the molecular structure shown in Fig. 2(b), which
has an overall arrangement of ligands similar to that in 2b
[Fig. 2(a)].
Complexes 4a and 4c, bridged by symmetric alkynes, display
only one 1H NMR signal for the methyl groups of the
(AsMe2)2O ligand whereas 4b displays two. Similarly, there is a
396
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single AsMe resonance at δ 23.0 in the 13C NMR spectrum of
4a and at δ 23.2 in the spectrum of 4c but there are two such
signals in the corresponding spectrum of 4b at δ 23.7 and 23.1.
These data indicate that the fluxional process described in detail
for 2c is again operative for 4a–c.
which renders the signal visible. Two peaks for the ipso-carbons
of the phenyl rings are visible in both spectra, indicating that
there are two environments for the phenyl groups.
(e) Reaction of [Co3(ꢀ3-CR)(CO)9] (R ؍ Cl or Me) with
As2Me4. Reaction of [Co3(µ3-CR)(CO)9] (R = Cl or Me) with
one equivalent of As2Me4 in toluene at 35 ЊC gave, in addition
to unreacted starting materials, deep purple [Co3(µ3-CR)-
{µ-(AsMe2)2O}(CO)7] (R = Cl (8a) (62%) or Me (8b)8 (59%)].
Both complexes are shown in Fig. 1. They have been character-
ised by IR, 1H and 13C NMR spectroscopy, mass spectrometry
and microanalysis. The molecular structure of [Co3(µ3-CCl)-
{µ-(AsMe2)2O}(CO)7] (8a) has been established by X-ray
diffraction and is shown in Fig. 6; this will be discussed later.
In the 1H spectra of both 8a and 8b, a pair of signals can be
seen which are attributed to the methyl groups of the bridging
ligand. These signals occur at δ 1.79 and 1.73 in the spectrum
of 8a and at δ 1.72 and 1.70 in that of 8b. Each resonance
integrates to six protons, which indicates that two distinct
methyl environments are present in each complex. In addition
to these signals, there is a further signal at δ 3.75 in the spectrum
of 8b, integrating to three protons, which is assigned to the
µ3-CMe group.
Two environments for the methyl groups of the ligand are
also indicated in the 13C NMR spectra. Sharp resonances with
approximately equal intensity are located at δ 24.9 and 19.7
in the spectrum of 8a and corresponding peaks appear in the
spectrum of 8b at δ 25.4 and 21.2. A single carbonyl resonance
is detected for each complex and in the case of complex 8b, the
apical µ3-C is resolved at δ 45.3. The corresponding peak in the
spectrum of 8a is not observed.
(c) Thermolysis of [Co2(ꢀ-PhCCPh){ꢀ-(AsMe2)2O}(CO)4]
(4a). Reflux of [Co2(µ-PhCCPh){µ-(AsMe2)2O}(CO)4] (4a)
in xylene for 24 h gave deep purple [Co2(µ-PhCCPh)-
{µ-(AsMe2)2O}2(CO)2] (5) (27%). The complex has been
characterised by IR, 1H and 13C NMR spectroscopy, mass
spectroscopy and microanalysis. The molecular structure of 5,
determined by X-ray crystallography, is shown in Fig. 3 and is
discussed later.
Although substitution of four carbonyl groups in complexes
of the type [Co2(µ-RCCRЈ)(CO)6] is not common, examples do
exist and the pattern and frequency of the recorded FT-IR
spectrum is typical of those reported in the literature for related
complexes.7 The 1H NMR spectrum of 5 shows resonances due
to the phenyl groups, which integrate to ten protons, and it also
exhibits two singlets at δ 1.59 and 1.47 which may be attributed
to the methyl groups of the bridging ligands. Clearly, in con-
trast to 4a, the fluxional process proposed for 2a can no longer
operate and there are now two distinct methyl environments;
two environments for the methyl groups on the bridging ligands
are also indicated in the 13C NMR by equal-intensity reson-
ances at δ 26.6 and 23.2.
The prolonged heating of [Co2(µ-PhCCPh){µ-(AsMe2)2O}-
(CO)4] (4a) results in a significant degree of decomposition and
it is the free (AsMe2)2O generated by this decomposition which
enables 5 to be formed. Under similar conditions Vahrenkamp
and Beurich reported that, in an alkylidyne tricobalt complex,
two coordinated (AsMe2)2O ligands produce the AsMe2–
O–AsMe–O–AsMe2 ligand via loss of AsMe2;8 this tridentate
ligand is coordinated at the three axial sites of the tricobalt
complex. In the alkyne dicobalt complex 5 the driving force
towards coupling of the two (AsMe2)2O ligands provided by
this potential mode of coordination is not present.
(f) Reaction of [(OC)3CO{ꢀ-C2(CO2Me)2}MoCp(CO)2] with
As2Ph4. The reaction of [(OC)3CO{µ-C2(CO2Me)2}MoCp-
(CO)2] with an excess of As2Ph4 in toluene at 35 ЊC gave
[{(HO)Ph2As}(OC)2Co{µ-C2(CO2Me)2}MoCp(CO)2] (9) in
43% yield, in addition to unreacted starting material. Complex
1
9, shown in Fig. 1, has been characterised by IR, H and 13C
NMR spectroscopy, mass spectrometry and microanalysis.
The molecular structure of 9 was determined by X-ray crystal-
lography and is shown in Fig. 7.
(d) Reaction of [Co3(ꢀ3-CR)(CO)9] (R ؍ Cl or Me) with
As2Ph4. Reaction of [Co3(µ3-CR)(CO)9] (R = Cl or Me) with one
equivalent of As2Ph4 in toluene at 40 ЊC gave, in addition to
unreacted starting materials, brown [Co3(µ3-CR)(CO)8(AsPh3)]
[R = Cl (6a) (18%)] and purple [Co3(µ3-CR){µ-(AsPh2)2O}-
(CO)7] [R = Cl (7a) (33%) or Me (7b) (22%)]. Proposed struc-
tures for the products are shown in Fig. 1. The complexes have
been characterised by IR spectroscopy and mass spectrometry.
1H and 13C NMR spectra and microanalytical data have been
obtained for complexes 7a and 7b and the molecular structures
of 7a and 7b have been determined by X-ray crystallography
and are shown in Figs. 4 and 5 respectively; the structures will be
discussed later.
The IR spectrum of 6a contains a number of pronounced
absorptions in the ν(CO) region. Reference to published IR
data9 suggests that the pattern and frequency of the bands
obtained is characteristic of a monosubstituted alkylidyne
tricobalt nonacarbonyl cluster. The mass spectrum shows a
molecular ion peak at 754 and signals corresponding to 1–8
carbonyl losses. These data are consistent with formulation of
the product as [Co3(µ3-CCl)(CO)8(AsPh3)].
There exists a number of derivatives of [(OC)3Co{µ-C2-
(CO2Me)2}MoCp(CO)2] obtained by substitution of the axial
carbonyl on cobalt by, for example, a tertiary phosphine5a,10
and these derivatives have infrared properties similar to those
recorded for 9. The mass spectroscopic and microanalytical
data also support the formula given above.
1
The H NMR spectrum of 9 exhibits, in addition to phenyl
resonances, singlets at δ 6.41, 5.45 and 3.48 with integrals of
1H, 5H and 6H, due to the OH, C5H5 and CO2Me groups,
respectively. The 13C NMR spectrum indicates carbonyl groups
bonded to molybdenum, giving rise to a sharp signal at δ 222.8
and carbonyl groups bonded to cobalt, which produce a broad
peak at δ 205. The spectrum also includes phenyl and cyclo-
pentadienyl carbon resonances, the latter occurring at δ 90.7
and singlets at δ 175.4, 72.8 and 52.7 assigned to the CO2Me,
CCO2Me and CO2Me carbon atoms, respectively.
(ii) X-Ray crystallographic studies
Phenyl resonances are seen in the 1H spectra of both 7a and
7b, with an additional singlet at δ 3.50, integrating to three
protons, in the spectrum of 7b. This is assigned to the apical
µ3-CMe group. A single broad peak due to the carbonyl carbon
atoms is observed in the 13C NMR spectra of both complexes.
In addition, the spectrum of 7b shows signals at δ 293.9 and
46.6 for the µ3-C and µ3-CMe carbon atoms respectively. A
signal for this alkylidyne carbon is often missing in 13C spectra
of such complexes,6 as it is in the spectrum of 7a; proximity of
the methyl group in 7b may be responsible for the enhancement
The X-ray structural studies show that [Co2(µ-PhCCH)-
{µ-(AsPh2)2O}(CO)4] (2b) and [Co2{µ-C2(CO2Me)2}{µ-
(AsMe2)2O}(CO)4] (4c) have very similar structures which are
illustrated in Fig. 2(a) and 2(b), respectively. Each maintains
the tetrahedral Co2C2 core formed by the alkyne ligand
coordinating in ‘side-on’ mode, with two equatorial carbonyl
ligands of the alkyne hexacarbonyldicobalt starting material
replaced by the arsenic atoms of a bridging (AsR2)O ligand.
Two carbonyl ligands remain on each cobalt atom of both
complexes, one located equatorially, the other occupying the
J. Chem. Soc., Dalton Trans., 2000, 395–405
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axial position. In the thermolysis product [Co2(µ-PhCCPh)-
{µ-(AsMe2)2O}2(CO)2] 5 (formed by 4a, the diphenylacetylene
analogue of 4c) a structure related to those of 2b and 4c is
observed but with the second µ-[(AsMe2)2O] ligand replacing
the remaining equatorial carbonyl ligands, so that 5 has only
one carbonyl ligand on each metal, both in axial sites. The
crystal of 5 has two molecules per equivalent position and these
both have the overall structure illustrated in Fig. 3 for molecule
1. Selected bond lengths and angles for these three related
compounds, 2b, 4c and 5, are listed in Table 1 for comparison.
The Co–Co bond lengths in the complexes are 2.484(1) Å
(2b), 2.493(1) Å (4c) and a mean of 2.488(3) Å (5) and these
are somewhat longer than that of 2.457(1) Å in [Co2(µ-
HCCH)(CO)4(PPh2SBun)2]11 where the dicobalt unit is bridged
only by an alkyne.
The Co–As bond lengths in the complexes have mean values
2.306(1) Å in 2b, 2.319(1) Å in 4c and 2.292(2) Å in 5; the small
but significant differences in these lengths may be related to
slight variations in π-back bonding from the metal. The methyl-
carboxylate substituents on the alkyne in 4c would be expected
to enhance its π-acid character relative to the PhCCH ligand in
2b and consistent with this the C(1)–C(2) alkyne bond in 4c is
0.057 Å longer than in 2b. Greater competition for available
π-electron density by the alkyne, and the fact that AsMe2 is a
weaker π-acceptor than AsPh2, is consistent with the greater
mean Co–As bond length in 4c, 2.319(1) Å compared to
2.306(1) Å in 2b. In the diphenylacetylene complex, 5, where
two strongly π-acidic carbonyl ligands have been replaced by a
second dimethylarsine oxide ligand, the shortest observed
mean Co–As distance of 2.292(2) Å is observed. The slight vari-
ations in individual Co–As bond lengths within each complex
although significant are not easily explained and may be related
to a sensitivity of this bond to small changes in conformation.
For example in molecule 1 of 5 the Co–As distances are in the
range 2.280(2)–2.296(2) (mean 2.288) Å and in molecule 2 are
consistently in the slightly higher range 2.285(2)–2.302(2) (mean
2.297) Å; one possible contributing factor to the differences
is the mean As–Co–As angle which is 105.3(1)Њ in molecule 1
compared to 107.2(1)Њ in molecule 2.
The mean As–O bonds within the diarsine ligands are
1.799(3) (2b), 1.803(5) (4c) and 1.803(8) Å (5) with correspond-
ing As–O–As angles of 118.4(2), 117.7(3) and 116.0(4)Њ (mean)
[cf. 1.67(3) Å and 137(2)Њ in free (AsPh2)2O12]. The changes
in these values compared to free (AsPh2)2O are consistent with
a reduction in pπ–dπ donation from oxygen to arsenic on
coordination of the As atom to the π-acidic metal.
Both the complexes [Co3(µ3-CR){µ-(AsPh2)2O}(CO)7]
[R = Cl (7a) and Me (7b)] have an approximately tetrahedral
core constituted by the capping of a tricobalt face by a µ3-CR
(R = Cl or Me) ligand (Figs. 4 and 5, respectively). Co(1) and
Co(2) are bridged equatorially by a bidentate (AsPh2)2O ligand
and each of these metal atoms is additionally ligated by two
carbonyl groups one located axially and the other equatorially.
Both equatorial sites and the axial position at Co(3) are occu-
pied by carbonyl groups.
Fig. 3 Molecular structure of [Co2(µ-PhCCPh){µ-AsMe2)2O}2(CO)2]
(5) including atom numbering scheme.
Table 1 Selected bond lengths (Å) and angles (Њ) for the dicobalt com-
pounds with bridging (AsR2)2O ligands (2b, 4c and 5)
5
2b
4c
Molecule 1 Molecule 2
Co(1)–Co(2)
Co(1)–As(1)
Co(1)–As(3)
Co(2)–As(2)
Co(2)–As(4)
Co(1)–C(1)
Co(1)–C(2)
Co(2)–C(1)
Co(2)–C(2)
mean Co–C (CO)
As(1)–O(1)
As(2)–O(1)
As(3)–O(2)
As(4)–O(2)
mean As–C
C(1)–C(2)
2.484(1) 2.493(1) 2.485(3)
2.302(1) 2.311(1) 2.296(2)
2.284(2)
2.309(1) 2.327(1) 2.290(2)
2.280(2)
1.950(6) 1.968(7) 1.92(1)
1.923(6) 1.926(6) 1.97(1)
1.954(5) 1.938(6) 1.96(1)
1.967(5) 1.939(7) 1.91(1)
1.773(7) 1.809(8) 1.77(1)
1.806(3) 1.822(5) 1.820(8)
1.791(3) 1.784(5) 1.804(8)
1.805(8)
2.490(3)
2.300(2)
2.299(2)
2.285(2)
2.302(2)
1.93(1)
1.93(1)
1.97(1)
1.93(1)
1.76(1)
1.794(8)
1.807(8)
1.802(8)
1.799(8)
1.95(2)
1.37(1)
1.50(1)
1.52(1)
1.791(8)
1.945(3) 1.949(8) 1.94(1)
1.339(7) 1.396(9) 1.36(1)
1.503(9) 1.48(1)
C(1)–C(11)
C(2)–C(21)
1.464(7) 1.472(9) 1.51(2)
As(1)–Co(1)–Co(2)
As(2)–Co(2)–Co(1)
As(3)–Co(1)–Co(2)
As(4)–Co(2)–Co(1)
As(1)–Co(1)–As(3)
As(2)–Co(2)–As(4)
As(1)–Co(1)–C(1)
As(1)–Co(1)–C(2)
As(1)–Co(1)–C(3)
As(1)–Co(1)–C(5)
As(2)–Co(2)–C(1)
As(2)–Co(2)–C(2)
As(2)–Co(2)–C(4)
As(2)–Co(2)–C(6)
As(3)–Co(1)–Co(2)
As(4)–Co(2)–Co(1)
As(3)–Co(1)–C(1)
As(3)–Co(1)–C(2)
As(3)–Co(1)–C(3)
As(4)–Co(2)–C(1)
As(4)–Co(2)–C(2)
As(4)–Co(2)–C(4)
Co(1)–As(1)–O(1)
Co(2)–As(2)–O(1)
Co(1)–As(3)–O(2)
Co(2)–As(4)–O(2)
As(1)–O(1)–As(2)
As(3)–O(2)–As(4)
98.83(5) 96.5(1)
95.30(4) 98.2(1)
95.45(9)
97.32(9)
98.61(9)
93.77(9)
105.4(1)
105.2(1)
94.72(9)
97.9(1)
98.02(9)
94.57(9)
106.97(1)
107.5(1)
106.4(4)
141.1(4)
101.7(5)
96.0(2)
135.6(2) 137.6(2) 142.0(4)
101.9(2) 98.1(3) 100.4(5)
103.6(2) 103.8(3)
103.2(2) 98.6(2)
138.6(2) 138.3(2) 137.2(4)
100.0(2) 97.1(3) 101.2(6)
107.7(2) 106.0(2)
98.1(2) 109.0(4)
97.4(4)
96.6(4)
136.2(4)
98.3(6)
The metallic triangle is not perfectly equilateral in either 7a
or 7b with metal–metal bonds in the ranges 2.502(2)–2.474(2) Å
in 7a and 2.4836(9)–2.4675(9) Å in 7b unlike the almost sym-
metrical range of 2.462(7)–2.475(7) Å in the unsubstituted
complex, [Co3(µ3-CMe)(CO)9].13 The bond between Co(3) and
the apical carbon is the longest of the three Co–C(1) bonds for
both complexes [1.927(9) Å in 7a; 1.941(4) Å in 7b].
The most notable difference in the molecular geometries of
7a and 7b is in the five-membered Co2As2O ring. The pen-
tagonal ring in 7b is almost symmetric, with Co–As bonds
measuring 2.2895(8) Å and 2.2853(8) Å and As–O bond lengths
of 1.802(3) Å and 1.808(3) Å. These distances are similar to
those determined for [Co3(µ-PhCCH){µ-(AsPh2)2O}(CO)4] (2b)
and the As–O–As angle of 114.1(1)Њ is also comparable with
that in 2b [118.4(2)Њ]. Both values for this angle contrast sharply
98.61(9)
93.77(9)
135.1(4)
94.9(4)
101.1(5)
139.4(4)
105.1(4)
101.2(6)
98.02(9)
94.57(9)
135.8(4)
95.2(4)
102.6(5)
139.8(4)
104.3(4)
100.3(6)
113.3(3)
112.8(3)
112.3(3)
112.9(3)
116.0(4)
115.9(4)
111.4(1) 112.8(2) 114.5(3)
114.4(1) 111.7(2) 113.3(3)
111.6(3)
114.3(3)
118.4(2) 117.7(3) 115.6(5)
116.3(4)
398
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Fig. 4 Molecular structure of [Co3(µ3-CCl){µ-(AsPh2)2O}(CO)7] (7a)
including atom numbering scheme.
Fig. 6 Molecular structure of [Co3(µ3-CCl){µ-(AsMe2)2O}(CO)7] (8a)
including atom numbering scheme.
Table 2 Bond lengths (Å) and angles (Њ) for the tricobalt compounds
with bridging (AsR2)2O ligands (7a, 7b and 8a)
7a
7b
8a
Co(1)–Co(2)
Co(1)–Co(3)
Co(2)–Co(3)
Co(1)–As(1)
Co(2)–As(2)
As(1)–O(1)
As(2)–O(1)
mean As–C
Co(1)–C(1)
Co(2)–C(1)
2.502(2)
2.474(2)
2.488(2)
2.293(2)
2.287(2)
1.921(7)
1.886(6)
1.926(6)
1.86(1)
1.86(1)
1.927(9)
1.76(1)
1.81(1)
1.77(1)
2.4836(9)
2.4784(8)
2.4675(9)
2.2895(8)
2.2853(8)
1.808(3)
1.802(3)
1.946(2)
1.895(4)
1.908(4)
1.941(4)
1.502(5)
1.816(5)
1.784(5)
2.478(2)
2.462(2)
2.459(2)
2.266(2)
2.264(2)
1.774(7)
1.788(7)
1.93(1)
1.841(9)
1.86(1)
1.90(1)
1.75(1)
1.81(1)
1.78(1)
Co(3)–C(1)
C(1)–Cl(1)/C(2)
mean Co–C (CO)ax
mean Co–C (CO)eq
Co(1)–Co(2)–Co(3)
Co(1)–Co(3)–Co(3)
Co(2)–Co(1)–Co(3)
As(1)–Co(1)–Co(2)
As(2)–Co(2)–Co(1)
Co(2)–Co(1)–C(1)
Co(3)–Co(1)–C(1)
Co(1)–Co(2)–C(1)
Co(3)–Co(2)–C(1)
Co(1)–Co(3)–C(1)
Co(2)–Co(3)–C(1)
Co(1)–As(1)–O(1)
Co(2)–As(2)–O(1)
As(1)–O(1)–As(2)
59.44(6)
60.57(6)
59.99(6)
96.51(6)
95.77(7)
47.8(3)
50.4(3)
47.6(3)
50.2(3)
47.9(3)
60.07(2)
60.28(2)
59.64(3)
95.87(3)
97.95(3)
49.4(1)
50.6(1)
49.0(1)
50.7(1)
48.9(1)
59.8(1)
60.5(1)
59.7(1)
98.6(1)
93.5(1)
48.3(3)
49.9(3)
47.6(3)
49.9(3)
47.8(3)
48.5(3)
112.2(2)
114.2(2)
115.9(4)
Fig. 5 Molecular structure of [Co3(µ3-CMe){µ-(AsPh2)2O}(CO)7] (7b)
including atom numbering scheme.
with that found in free (AsPh2)2O [137(2)Њ],12 the reasons for the
compression of the angle on coordination having been covered
in the discussion of the structure of 2b.
47.7(3)
49.5(1)
113.4(2)
115.4(2)
108.8(4)
112.76(9)
111.76(8)
114.4(1)
The As–O–As angle in 7a is, however, significantly smaller
[108.8(4)Њ] than that in 2b or in 7b and the As–O bonds are
longer in 7a [1.886(6) and 1.921(7) Å] than in 7b. It is surprising
that complexes 2b and 7b, with obvious differences in their
molecular cores, have Co2As2O rings with similar geometries,
whilst larger differences in geometry are seen in the Co2As2O
rings of complexes 7a and 7b, whose cores are almost identical.
There appears to be no electronic or geometric explanation of
this observation.
Despite the difference described above, the mean Co–Co–As
angles remain constant within the given error limits (96.14Њ in
7a; 96.91Њ in 7b cf. 97.07Њ in 2b) and the Co–As bond lengths for
7a and 7b are also practically identical.
Table 2 for comparison. The structure features a tetrahedral
Co3C core, formed by the capping of a tricobalt face by a chloro-
methylidyne ligand, µ3-CCl. This core is the same as that of 7a;
indeed the overall structure is closely comparable to that of 7a
and it will not be discussed in detail for that reason. It is worth
noting that the bridged Co–Co bond is the longest of the three
M–M bonds in the complex, which was also found to be the
case for complexes 7a and 7b. At 2.478(2) Å, it is, however,
significantly shorter than the corresponding bond in 7a
[2.502(2) Å]. The geometry of the arsine oxide ligand is com-
parable to that for the same ligand in complex 4c. The As–O
bond lengths are 1.788(7) Å and 1.774(7) Å [cf. 1.822(5) and
1.784(5) Å in 4c] and the angle at oxygen is 115.9(4)Њ [117.7(3)Њ
The molecular structure of [Co3(µ3-CCl){µ-(AsMe2)2O}-
(CO)7] (8a) is presented in Fig. 6. Selected bond lengths and
angles for the three related complexes 8a, 7a and 7b are listed in
J. Chem. Soc., Dalton Trans., 2000, 395–405
399

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as compared with cobalt. These values also show that in this
complex, the alkyne lies approximately perpendicular to the
Co–Mo bond without any significant degree of twisting.
The angle of 149.8(4)Њ between the Mo–Co and Co–As
bonds is fairly typical given that the arsine occupies the axial
site. The Co–As bond measures 2.312(1) Å and the As–O bond
is 1.770(5) Å in length which indicates that this is an As–O
single bond and not an As᎐O bond. These data are compar-
᎐
able with those determined for [(dmgH)2ClCo(AsPh2OH)]14
[Co–As 2.322(1) Å; As–O 1.781(7) Å]. Given that this complex
contains the AsPh2OH ligand coordinated to Co(), it is
unsurprising that the Co–As bond in which the cobalt has a
formal oxidation state of zero is somewhat shorter.
The geometry about arsenic is that of a distorted tetra-
hedron. The angles between the Co–As bond and the three
remaining bonds to arsenic are in the range 115.2(1) to
121.4(1)Њ, whereas angles between these latter three bonds are
compressed to 98.5(3)–100.3(3)Њ.
Fig.
7
Molecular structure of [{(HO)Ph2As}(OC)2Co{µ-C2(CO2-
Me)2}MoCp(CO)2] (9) including atom numbering scheme.
(iii) Reaction pathways
Table 3 Selected bond lengths (Å) and angles (Њ) for [{(OH)Ph2As}-
(OC)2Co{µ-C2(CO2Me)2}MoCp(CO)2] (9)
The major product in the above reactions with homometallic
clusters is typically a complex featuring a single bis-diarsine
oxide ligand bridging a Co–Co bond. Formation of such
products is immediately reminiscent of the work of Vahrenkamp
and Beurich8 in which the aminoarsine, AsMe2NMe2, was
used to produce mono- and bis-substituted derivatives of alkyl-
idyne tricobalt nonacarbonyl complexes. These derivatives
were found to be extremely sensitive to hydrolysis, giving
complexes which featured a bridging (AsMe2)2O ligand. The
same research group found that the mononuclear complex,
(OC)5W–AsMe2Cl, reacted with H2O to give the binuclear
complex (OC)5W–AsMe2–O–AsMe2–W(CO)5.15 Chromato-
graphy on silica was found to be sufficient to convert the
complex, (OC)4Fe–AsMe2Cl to (OC)4Fe–AsMe2–O–AsMe2–
Fe(CO)4.16 More recently, it has been shown that both P2Ph4
and PPh2H can react with alkylidyne tricobalt nonacarbonyl
clusters to yield products with bridging (PPh2)2O ligands.6
The proposed pathway for the formation of complexes con-
taining the (AsR2)2O ligand from As2R4 is shown in Fig. 8 for
the reactions with [Co(µ-RCCRЈ)(CO)6]. It seems likely that
mono-substitution by As2R4 will initially give intermediate A.
Stable complexes of this type have been isolated from reactions
of the alkyne-bridged dicobalt complex with P2Ph4.17 The
As2R4 ligand in the substituted complex could then attack the
second cobalt centre to give a µ-As2R4 intermediate B. Again
stable complexes of this type have been isolated in the corre-
sponding reactions with P2Ph4 although an alternative
intermediate C, which involves substitution by a second As2R4
ligand cannot be excluded. The next step, which has no parallel
in the corresponding reactions with P2Ph4 could involve
the hydrolytic/oxidative reaction of either B or C to give a
bis-AsR2(OH)-substituted intermediate D. Condensation of
the two AsR2OH ligands with elimination of H2O would then
give the observed µ-(AsR2)2O products. Although the reactions
were carried out under anhydrous and anaerobic conditions,
work up in air on silica, which can contain small quantities of
water, most likely effects the hydrolysis/oxidation, as has been
observed in a number of other cases.6,16 An analogous pathway
is proposed for the tricobalt systems and in this case the
hydrolytic/oxidative process does have precedents in the con-
version of AsMe2NMe2, PPh2H or P2Ph4 to (AsMe2)2O or
(PPh2)2O on reaction with these trimetallic clusters.6,8
Co(1)–Mo(1)
Co(1)–C(2)
Mo(1)–C(2)
As(1)–O(1)
As(1)–C(51)
2.704(1)
1.956(5)
2.140(5)
1.770(4)
1.951(3)
Co(1)–C(1)
Mo(1)–C(1)
As(1)–Co(1)
As(1)–C(31)
C(1)–C(2)
1.960(5)
2.138(5)
2.312(1)
1.943(3)
1.383(7)
Co(1)–Ccarbonyl
Mo(1)–Ccarbonyl
C–O
1.785(7), 1.796(7)
1.997(7), 2.024(7)
1.135(7)–1.147(7)
C(1)–Mo(1)–Co(1)
C(2)–Mo(1)–C(1)
C(1)–Co(1)–Mo(1)
C(1)–Co(1)–C(2)
45.9(1)
37.7(2)
51.6(2)
41.4(2)
C(2)–Mo(1)–Co(1)
As(1)–Co(1)–Mo(1) 149.8(4)
C(2)–Co(1)–Mo(1)
Co(1)–As(1)–O(1)
Co(1)–As(1)–C(31) 121.4(1)
C(2)–C(1)–Mo(1)
Co(1)–C(2)–Mo(1)
C(1)–C(2)–Co(1)
C(1)–C(2)–C(21)
45.8(1)
51.7(2)
115.2(1)
Co(1)–As(1)–C(31) 118.82(7)
Co(1)–C(1)–Mo(1)
C(2)–C(1)–Co(1)
C(1)–C(2)–Mo(1)
C(2)–C(1)–C(11)
82.5(2)
69.2(3)
71.1(3)
134.2(5)
71.2(3)
82.5(2)
69.5(3)
129.7(5)
in 4c]. The Co–As bond lengths in 8a are equal [2.264(2) and
2.266(2) Å] within the limits of experimental error but the
reason why they should be so much shorter than the corre-
sponding bonds in 4c [2.327(1) and 2.311(1) Å] is unclear.
The structure of [{(HO)Ph2As}(OC)2Co{µ-C2(CO2Me)2}-
MoCp(CO)2] (9) is shown in Fig. 7. Selected bond lengths and
angles are presented in Table 3. A dimethylacetylene dicarbox-
ylate ligand coordinates to the cobalt–molybdenum fragment in
the ‘side-on’ mode such that the acetylenic and Co–Mo bonds
are almost perpendicular. The core of this molecule is thus a
CoMoC2 tetrahedron. The cyclopentadienyl ligand is bonded
to molybdenum on the opposite side of the molecule to the
acetylenic ‘edge’. Two carbonyl groups also ligate this metal
atom. The cobalt atom carries two carbonyl ligands, which
occupy equatorial sites. The axial carbonyl has been replaced by
a molecule of diphenylarsinous acid, AsPh2OH, which bonds
to cobalt via the arsenic atom.
The CoMoC2 core is distorted from a regular tetrahedron.
Firstly, the Co–Mo and acetylenic bonds are obviously of
different lengths. The Co–Mo distance of 2.704(1) Å is within
the range expected for Co–Mo bond in complexes such as this
(2.60–2.75 Å).5a The acetylenic bond [1.383(7) Å] is also of a
length typical for DMAD (dimethyl acetylenedicarboxylate)
coordinating a bimetallic unit in this fashion.4 The alkyne does
not lie equidistant from both metal centres. Rather, it is
displaced away from molybdenum and towards cobalt, leading
to Co–CDMAD bond lengths of 1.960(5) Å and 1.956(5) Å and
Mo–CDMAD bond lengths of 2.140(5) Å and 2.138(5) Å. This
observation is in accord with the larger radius of molybdenum
This hydrolytic/oxidative mechanism is further supported
by the reaction of As2Ph4 with the DMAD-bridged cobalt–
molybdenum complex, which yields as the sole isolable product
a mono-AsPh2OH-substituted complex (9) in which the arsine
ligand occupies the axial site at cobalt. At the temperature
employed in this reaction, substitution at molybdenum does not
occur but substitution of As2Ph4 at cobalt presumably occurs as
400
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suggests that oxidation of the diarsine does not occur before
interaction with the cluster. Given the rigorous exclusion of
oxygen during the reaction, it is unlikely that the oxidation of
the ligand occurs prior to work up and the proposed conversion
of the coordinated arsine to a µ-(AsR2)2O ligand has a pre-
cedent in the work of Vahrenkamp.
Disproportionation of diarsines is a known reaction, yielding
tertiary arsines and elemental arsenic at high temperatures.
Tetraphenyldiarsine, for example, has been reported to dis-
proportionate in this way at 300 ЊC in vacuo.20
300 ЊC
3As2Ph4
2As ϩ 4AsPh3
in vacuo
The isolation of mono-AsR3-substituted complexes in some of
the reactions studied suggests that the disproportionation
reaction can occur at ambient temperatures when As2R4 is
coordinated to a transition metal. This may occur as shown
below:
The fate of the AsR groups, excised in reactions of this type has
been discussed by Rheingold and Di Maio.21 Disproportiona-
tion into elemental arsenic and AsR2 groups with dimerisation
of the latter to generate diarsines is the preferred process.
2AsR → As ϩ AsR2
2AsR2 → As2R4
Conclusions
The above reactions show that the diarsines As2R4 (R = Me or
Ph) react differently from the diphosphine P2Ph4 with alkyne-
bridged dicobalt systems. While E–E bond cleavage is apparent
for E = P or As, in the case of E = As arsenido-bridged products
are not isolated as they are for E = P nor are cobaltacyclic com-
plexes isolated in which AsR2 has combined with the bridging
organic ligand in the way that PR2 fragments are known to do.17
Rather, As–O bond formation is the preferred process and it has
been possible to isolate in good yield and structurally character-
ise a number of complexes that possess µ-(AsR2)2O ligands.
This is also observed where diarsines react with alkylidyne
tricobalt clusters and in this case the outcome parallels that
obtained when these clusters are reacted with diphosphines.6
Fig. 8 Possible mechanism for formation of bis-arsine oxide-bridged
complexes. (i) As2R4 [R = Me or Ph], heat.
it did for the homometallic complexes and is then followed by
cleavage of the As–As bond in a hydrolytic/oxidative process
that generates two molecules of the arsenous acid, AsPh2(OH),
one coordinated to cobalt and one free. Since in this instance
there is no equivalent ligand bound to the adjacent metal
centre, condensation to form the (AsPh2)2O ligand is not pos-
sible and the AsPh2(OH)-substituted species can therefore be
isolated as the stable complex 9. While esters of the arsenous
acids have been isolated, the free acids themselves are not fully
characterised18 and only one other complex containing an
AsPh2OH ligand has had its structure determined.14
Experimental
An alternative route to the (AsPh2)2O complexes would
involve air-oxidation of the free diarsines prior to their
coordination; the oxidised ligand could then simply coordinate
to afford the isolated products. Although the controlled oxid-
ation of diarsines19,20 is known to generate (AsR2)2O, if
(AsR2)2O existed in solution prior to interaction with the
cluster, a product with a ‘pendant’ (AsR2)2O ligand would be
expected. Although the absence of such species in the case of
the homometallic clusters could be explained by their facile
conversion to the bridged products isolated, in the Co–Mo
system formation of bridged products does not appear to be
possible and the absence of ‘pendant’ (AsR2)2O products here
All reactions were carried out under an atmosphere of dry,
oxygen free nitrogen, using solvents that were freshly distilled
from the appropriate drying agent. Ultraviolet irradiation
experiments were performed using a 125 W Hanovia medium
pressure mercury vapour lamp.
Infrared spectra were recorded in n-hexane or CH2Cl2 solu-
tion in 0.5 mm NaCl cells, using a Perkin-Elmer Paragon 1000
Fourier-Transform spectrometer or a Perkin-Elmer 1600 series
spectrometer. Fast atom bombardment mass spectra were
obtained on a Kratos MS890 instrument. Fast ion bombard-
ment mass spectra were obtained on a Kratos MS50 instru-
1
ment. Nitrobenzyl alcohol was used as a matrix. H and 13C
J. Chem. Soc., Dalton Trans., 2000, 395–405
401

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NMR spectra were recorded on Bruker AM400 or WM250
spectrometers using the solvent resonance as an internal
standard. Microanalyses were performed by the Microanalyti-
cal Department, University of Cambridge.
of the reaction solvent under vacuum, the residue was dissolved
in the minimum quantity of CH2Cl2 and adsorbed onto silica.
The silica was pumped dry and transferred to the top of a silica
chromatography column. Elution with hexane/CH2Cl2 (4:1)
gave unreacted [Co2(µ-MeCCH)(CO)6] (20 mg), [Co2(µ-
MeCCH){µ-(AsPh2)2O}(CO)4] (2c) (476 mg, 43%). Complex 2c
(Found: C, 49.43; H, 3.11. C31H24As2Co2O5 requires C, 50.03;
H, 3.25%). Mass spectrum, m/z 744 (Mϩ) and Mϩ Ϫ nCO
(n = 1–4). νmax/cmϪ1 (CH2Cl2), 2028m, 1998s, 1971m. NMR
Preparative thin layer chromatography was carried out on
1 mm plates prepared at the University Chemical Laboratory,
Cambridge. Column chromatography was performed on
Kieslgel 60 (70–230 mesh). Products are given in order of
decreasing Rf values. Unless otherwise stated, all reagents were
obtained from commercial suppliers and used without further
purification. The compounds [Co2(µ-RCCRЈ)(CO)6]22 (R = RЈ =
CO2Me, Ph; R = H, RЈ = Ph, Me), [Co3(µ3-CR)(CO)9]23
(R = Me or Cl) and [(OC)3Co{µ-C2(CO2Me)2}MoCp(CO)2]24
were prepared by literature methods.
1
(CDCl3), H, δ 7.5–7.4 [m, 20H, Ph], 5.47 [s, 1H, CH], 2.68 [s,
3H, CMe]; 13C, δ 205.8 [s, 2CO], 202.7 [s, 2CO], 143.4–128.6
[Ph], 103.4 [s, CMe], 73.6 [s, CH], 22.5 [s, CMe].
(iv) Reaction of [Co2(ꢀ-PhCCPh)(CO)6] and As2Me4
25
The diarsine As2Me4 was prepared by reduction of
cacodylic acid [Me2As(O)(OH)]. The oxide, (AsPh2)2O,26,27 was
synthesised by reaction of PhMgBr and As2O3. Treatment of
this oxide with HCl generated AsPh2Cl.27,28 Coupling of
AsPh2Cl and LiAsPh229 afforded As2Ph4.30
[Co2(µ-PhCCPh)(CO)6] (500 mg, 108 mmol) and As2Me4 (250
mg, 1.19 mmol) were dissolved in toluene (60 ml) and heated
at 40 ЊC for 15 h. After removal of the reaction solvent under
vacuum, the residue was dissolved in a minimum quantity of
CH2Cl2 and adsorbed onto silica. The silica was pumped dry
and transferred to the top of a silica chromatography column.
Elution with hexane/CH2Cl2 (3:2) gave red-brown [Co2(µ-
PhCCPh)(CO)5(AsMe3)] (3a) (75 mg, 12%), two products in
very minor yield which were not collected and deep purple,
crystalline [Co2(µ-PhCCPh){µ-(AsMe2)2O}(CO)4] (4a) (147
mg, 21%). Crystals of 3a suitable for diffraction were grown by
slow evaporation at 0 ЊC of an n-hexane/CH2Cl2 solution of
the complex. Complex 3a (Found: C, 47.31; H, 3.36. C22H19-
AsCo2O5 requires C, 47.51; H, 3.44%). Mass spectrum, m/z 556
(Mϩ) Mϩ Ϫ nCO (n = 1–5). νmax/cmϪ1 (CH2Cl2), 2058s, 2006vs,
1998 (sh), 1958w, 1606w. NMR (CDCl3), 1H, δ 7.7–7.2 [m, 10H,
Ph], 1.47 [s, 9H, Me]; 13C, δ 204.7 [s, 2CO], 200.9 [s, 3CO],
140.7–126.7 [Ph], 86.1 [s, CPh], 29.7 [s, Me]. Complex 4a
(Found: C, 40.20; H, 3.45. C22H22AsCo2O5 requires C, 41.67;
H, 3.50%). Mass spectrum, m/z 634 (Mϩ) and Mϩ Ϫ nCO (n =
1–4). νmax/cmϪ1 (CH2Cl2), 2026s, 1997vs, 1970s, 1604w. NMR
(i) Reaction of [Co2(ꢀ-PhCCPh)(CO)6] and As2Ph4
[Co2(µ-PhCCPh)(CO)6] (250 mg, 0.54 mmol) and As2Ph4 (4 ml,
0.15 M in toluene, 0.6 mmol) were dissolved in toluene (60 ml)
and heated at 40 ЊC with stirring for 9 h. After removal of the
reaction solvent under vacuum, the residue was dissolved in the
minimum quantity of CH2Cl2 and applied to the base of silica
TLC plates. Elution with hexane/CH2Cl2 (4:1) gave unreacted
[Co2(µ-PhCCPh)(CO)6] (51 mg), green [Co2(µ-PhCCPh)(CO)5-
(AsPh3)] (1a) (16 mg, 4%), purple [Co2(µ-PhCCPh){µ-
(AsPh2)2O}(CO)4] (2a) (287 mg, 60%). Complex 1a (Found: C,
59.86; H, 3.48. C37H25AsCo2O5 requires C, 59.86; H, 3.39%).
Mass spectrum, m/z 742 (Mϩ) and Mϩ Ϫ nCO (n = 1–5). νmax
/
cmϪ1 (CH2Cl2), 2061s, 2012s, 2001 (sh), 1961w. NMR (CDCl3),
1H, δ 7.4–6.7 [m, 25H, Ph]; 13C, δ 140.1–126.5 [Ph], 86.3 [s,
CPh]. Complex 2a (Found: C, 56.85; H, 3.33. C42H30As2Co2O5
requires C, 57.17; H, 3.43%). Mass spectrum, m/z 882 (Mϩ)
and Mϩ Ϫ nCO (n = 1–4). νmax/cmϪ1 (CH2Cl2), 2030m, 2003s,
1977m. NMR (CDCl3), 1H, δ 7.5–7.0 [m, 30H, Ph]; 13C, δ 203.1
[s, CO], 142.9–126.3 [Ph].
1
(CDCl3), H, δ 7.5–7.3 [m, 10H, Ph], 1.58 [s, 12H, Me]; 13C,
δ 203.5 [s, CO], 142.0–126.0 [Ph], 95.3 [s, CPh], 23.0 [s, Me].
(v) Reaction of [Co2(ꢀ-PhCCH)(CO)6] and As2Me4
[Co2(µ-PhCCH)(CO)6] (740 mg, 1.91 mmol) and As2Me4 (410
mg, 1.95 mmol) were dissolved in toluene (60 ml) and heated at
40 ЊC for 24 h. After removal of the reaction solvent under
vacuum, the residue was dissolved in the minimum quantity of
CH2Cl2 and applied to the base of silica TLC plates. Elution
with hexane/CH2Cl2 (4:1) gave purple [Co2(µ-PhCCH)-
(CO)5(AsMe3)] (3b) (156 mg, 17%), a trace of a yellow-brown
product which was not collected and deep purple, crystalline,
[Co2(µ-PhCCH){µ-(AsMe2)2O}(CO)4] (4b) (200 mg, 18%).
Complex 3b. Mass spectrum, m/z 480 (Mϩ) and Mϩ Ϫ nCO
(n = 1–5). νmax/cmϪ1 (CH2Cl2), 2062s, 2007vs, 1996 (sh), 1959m,
(ii) Reaction of [Co2(ꢀ-PhCCH)(CO)6] and As2Ph4
[Co2(µ-PhCCH)(CO)6] (1.093 g, 2.82 mmol) and As2Ph4 (18.8
ml, 0.15 M in toluene, 2.82 mmol) were dissolved in toluene (60
ml) and heated at 40 ЊC with stirring for 15 h. After removal of
the reaction solvent under vacuum, the residue was dissolved in
the minimum quantity of CH2Cl2 and adsorbed onto silica. The
silica was pumped dry and transferred to the top of a silica
chromatography column. Elution with hexane/CH2Cl2 (4:1)
gave unreacted [Co2(µ-PhCCH)(CO)6] (116 mg), brown-green
[Co2(µ-PhCCH)(CO)5(AsPh3)] (1b) (368 mg, 20%) and pur-
ple [Co2(µ-PhCCH){µ-(AsPh2)2O}(CO)4] (2b) (227 mg, 10%).
Crystals of 2b suitable for diffraction were grown by slow
evaporation at 0 ЊC of an n-hexane/CH2Cl2 solution of the
complex. Complex 1b (Found: C, 55.77; H, 3.11. C31H21As-
Co2O5 requires C, 55.88; H, 3.18%). Mass spectrum, m/z 666
(Mϩ) and Mϩ Ϫ nCO (n = 1–5). νmax/cmϪ1 (hexane), 2063m,
2012s, 2002 (sh), 1961w. NMR (CDCl3), 1H, δ 8.0–6.5 [m, 20H,
Ph], 5.69 [s, 1H, CH]; 13C, δ 139.6–128.5 [Ph]. Complex 2b
(Found: C, 53.76; H, 3.18. C36H26As2Co2O5 requires C, 53.63;
H, 3.25%). Mass spectrum, m/z 806 (Mϩ) and Mϩ Ϫ nCO
(n = 1–4). νmax/cmϪ1 (CH2Cl2), 2031m, 2004s, 1977m. NMR
1
1606w. NMR (CDCl3), H, δ 7.7–7.3 [m, 5H, Ph], 5.85 [s, 1H,
CH], 1.44 [s, 9H, Me]; 13C, δ 205.4 [s, 1CO], 204.7 [s, 1CO],
201.2 [s, 3CO], 139.9–126.6 [Ph], 84.8 [s, CPh], 68.2 [s, CH], 32.6
[s, Me]. Complex 4b (Found: C, 34.10; H, 3.17. C16H18As2Co2O5
requires C, 34.44; H, 3.25%). Mass spectrum, m/z 558 (Mϩ)
and Mϩ Ϫ nCO (n = 1–4). νmax/cmϪ1 (CH2Cl2), 2027m, 1997vs,
1
1969s. NMR (CDCl3), H, δ 7.5–7.2 [m, 5H, Ph], 5.84 [s, 1H,
CH], 1.67 [s, 3H, Me], 1.62 [s, 3H, Me]; 13C, δ 205 [s, 2CO], 202
[s, 2CO], 141.9–126.4 [Ph], 98.5 [s, CPh], 72.2 [s, CH], 23.7 [s,
Me], 23.1 [s, Me].
1
(CDCl3), H, δ 7.7–7.1 [m, 25H, Ph], 5.75 [s, 1H, CH]; 13C,
(vi) Reaction of [Co2{ꢀ-C2(CO2Me)2}(CO)6] and As2Me4
δ 143.2–126.9 [Ph], 70.5 [s, CH].
[Co2{µ-C2(CO2Me)2}(CO)6] (520 mg, 1.21 mmol) and As2Me4
(260 mg, 1.23 mmol) were dissolved in toluene (60 ml) and
heated at 35 ЊC for 15 h. After removal of the reaction solvent
under vacuum, the residue was dissolved in the minimum quan-
tity of CH2Cl2 and applied to the base of silica TLC plates.
Elution with hexane/ethyl acetate (7:3) gave orange [Co2{µ-
(iii) Reaction of [Co2(ꢀ-MeCCH)(CO)6] and As2Ph4
[Co2(µ-MeCCH)(CO)6] (726 mg, 2.23 mmol) and As2Ph4 (14.9
ml, 0.15 M in toluene, 2.24 mmol) were dissolved in toluene (60
ml) and heated at 40 ЊC with stirring for 9 hours. After removal
402
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C2(CO2Me)2}(CO)5(AsMe3)] (3c) (160 mg, 25%) and deep red,
crystalline [Co2{µ-C2(CO2Me)2}{µ-(AsMe2)2O}(CO)4] (4c) (252
mg, 35%). Crystals of 4c suitable for diffraction were grown by
slow evaporation at 0 ЊC of an n-hexane/CH2Cl2 solution of
the complex. Complex 3c (Found: C, 32.24; H, 2.87. C14H15-
AsCo2O9 requires C, 32.33; H, 2.91%). Mass spectrum, m/z 520
(Mϩ) and Mϩ Ϫ nCO (n = 1–5). νmax/cmϪ1 (CH2Cl2), 2082s,
2033vs, 2021s, 1985m, 1704m. NMR (CDCl3), 1H, δ 3.79 [s, 6H,
CO2Me], 1.34 [s, 9H, AsMe]; 13C, δ 203 [s, 2CO], 199 [s, 3CO],
172.0 [s, CO2Me], 73.4 [s, CCO2Me], 52.7 [s, CO2Me], 13.7 [s,
AsMe]. Complex 4c (Found: C, 27.90; H, 2.92. C14H18As2Co2O9
requires C, 28.12; H, 3.03%). Mass spectrum, m/z 598 (Mϩ) and
Mϩ Ϫ nCO (n = 1–4). νmax/cmϪ1 (CH2Cl2), 2059s, 2023vs, 1997s,
1698m. NMR (CDCl3), 1H, δ 3.80 [s, 6H, CO2Me], 1.69 [s, 12H,
Me]; 13C, δ 200.8 [s, CO], 172.6 [s, CO2Me], 79.2 [s, CCO2Me],
52.6 [s, CCO2Me], 23.2 [s, AsMe].
Mϩ Ϫ nCO (n = 1–7). νmax/cmϪ1 (CH2Cl2), 2062m, 2009s. NMR
1
(CDCl3), H, δ 7.7–7.2 [m, 20H, Ph], 3.50 [s, 3H, Me]; 13C,
δ 293.9 [s, µ3-CMe], 203.7 [s, CO], 142.8–128.8 [Ph], 46.6 [s,
CMe].
(x) Reaction of [Co3(ꢀ3-CCl)(CO)9] and As2Me4
[Co3(µ3-CCl)(CO)9] (345 mg, 0.72 mmol) and As2Me4 (160 mg,
0.76 mmol) were dissolved in 60 ml toluene and heated at 35 ЊC
for 3 h. After removal of reaction solvent under vacuum, the
residue was dissolved in a minimum quantity of CH2Cl2 and
adsorbed onto silica. The silica was pumped dry and trans-
ferred to the top of a silica chromatography column. Elution
with hexane/CH2Cl2 (4:1) gave unreacted [Co3(µ3-CCl)(CO)9]
and deep purple, crystalline [Co3(µ3-CCl){µ-(AsMe2)2O}(CO)7]
(8a) (289 mg, 62%). Crystals of 8a suitable for diffraction were
grown by slow evaporation at 0 ЊC of an n-hexane/CH2Cl2 solu-
tion of the complex. Complex 8a (Found: C, 22.42; H, 2.04.
C12H12As2ClCo3O8 requires C, 22.30; H, 1.87%). Mass spec-
trum, m/z 646 (Mϩ) and Mϩ Ϫ nCO (n = 1–7). νmax/cmϪ1
(CH2Cl2), 2072m, 2022vs, 2005w, 1994w, 1982w. NMR
(CDCl3), 1H, δ 1.79 [s, 6H, Me], 1.73 [s, 6H, Me]; 13C, 202.5 [s,
CO], 24.9 [s, Me], 19.7 [s, Me].
(vii) Thermolysis of [Co2(ꢀ-PhCCPh){ꢀ-(AsMe2)2O}(CO)4] (4a)
[Co2(µ-PhCCPh){µ-(AsMe2)2O}(CO)4] (4a) (405 mg, 0.64
mmol) was dissolved in xylene (60 ml) and refluxed for 24 h.
After removal of reaction solvent under vacuum, the residue
was dissolved in a minimum quantity of CH2Cl2. TLC of this
showed it to contain one product only. By recrystallisation from
CH2Cl2, deep purple, [Co2(µ-PhCCPh){µ-(AsMe2)2O}2(CO)2]
(5) (140 mg, 27%) was recovered. Crystals suitable for dif-
fraction were grown by slow evaporation at 0 ЊC of a CH2Cl2
solution of the complex. Complex 5 (Found: C, 35.74; H, 4.14.
C24H34As4Co2O4 requires C, 35.85; H, 4.26%). Mass spectrum,
m/z 804 (Mϩ) and Mϩ Ϫ nCO (n = 1–2). νmax/cmϪ1 (CH2Cl2),
(xi) Reaction of [Co3(ꢀ3-CMe)(CO)9] and As2Me4
[Co3(µ3-CMe)(CO)9] (330 mg, 0.72 mmol) and As2Me4 (160 mg,
0.76 mmol) were dissolved in 60 ml toluene and heated at 40 ЊC
for 5 h. After removal of reaction solvent under vacuum, the
residue was dissolved in a minimum quantity of CH2Cl2 and
adsorbed onto silica. The silica was pumped dry and trans-
ferred to the top of a silica chromatography column. Elution
with hexane/CH2Cl2 (1:1) gave deep purple, crystalline [Co3(µ3-
CMe){µ-(AsMe2)2O}(CO)7] (8b) (266 mg, 59%). Complex 8b
(Found: C, 24.76; H, 2.31. C13H15As2Co3O8 requires C, 24.95;
H, 2.42%). Mass spectrum, m/z 626 (Mϩ) and Mϩ Ϫ nCO
(n = 1–7). νmax/cmϪ1 (CH2Cl2), 2064m, 2010s, 1990w. NMR
(CDCl3), 1H, δ 3.75 [s, 3H, CMe], 1.72 [s, 6H, Me], 1.70 [s, 6H,
Me]; 13C, δ 203.9 [s, CO], 45.3 [s, CMe], 25.4 [s, AsMe], 21.2 [s,
AsMe].
1
1940 (sh), 1925s. NMR (CDCl3), H, δ 7.4–7.1 [m, 10H, Ph],
1.59 [s, 12H, Me], 1.47 [s, 12H, Me]; 13C, δ 145.5–127.8 [Ph],
97.0 [s, CPh], 26.6 [s, Me], 23.2 [s, Me].
(viii) Reaction of [Co3(ꢀ3-CCl)(CO)9] and As2Ph4
[Co3(µ3-CCl)(CO)9] (920 mg, 1.93 mmol) and As2Ph4 (13 ml,
0.15 M in toluene, 1.95 mmol) were dissolved in toluene (60 ml)
and heated at 40 ЊC with stirring for 4 h. After removal of the
reaction solvent under vacuum, the residue was dissolved in
the minimum quantity of CH2Cl2 and adsorbed onto silica. The
silica was pumped dry and transferred to the top of a silica
chromatography column. Elution with hexane/CH2Cl2 (4:1)
gave unreacted [Co3(µ3-CCl)(CO)9] (300 mg, 33%), brown
[Co3(µ3-CCl)(CO)8(AsPh3)] (6a) (264 mg, 18%) and purple
[Co3(µ3-CCl){µ-(AsPh2)2O}(CO)7] (7a) (563 mg, 33%). Crystals
of 7a suitable for diffraction were grown by slow evaporation at
0 ЊC of an n-hexane/CH2Cl2 solution of the complex. Complex
6a. Mass spectrum, m/z 754 (Mϩ) and Mϩ Ϫ nCO (n = 1–8).
νmax/cmϪ1 (hexane), 2085s, 2062m, 2043s, 2032s, 2023s, 2004m,
1979w. Complex 7a (Found: C, 42.72; H, 2.23. C32H20As2Cl-
Co3O8 requires C, 42.96; H, 2.25%). Mass spectrum, m/z 894
(Mϩ) and Mϩ Ϫ nCO (n = 1–7). νmax/cmϪ1 (CH2Cl2), 2071m,
(xii) Reaction of [(OC)3Co{ꢀ-C2(CO2Me)2}MoCp(CO)2] and
As2Ph4
[(OC)3Co{µ-C2(CO2Me)2}MoCp(CO)2] (785 mg, 1.56 mmol)
and As2Ph4 (31 ml, 0.15 M in toluene, 4.65 mmol) were dis-
solved in 60 ml toluene and heated at 35 ЊC with stirring for
24 h. After removal of the reaction solvent under vacuum the
residue was dissolved in the minimum quantity of CH2Cl2 and
applied to the base of silica TLC places. Elution with hexane/
acetone (3:1) gave, in addition to unreacted starting material,
red-orange
[{(HO)Ph2As}(OC)2Co{µ-C2(CO2Me)2}MoCp-
(CO)2] (9) (514 mg, 43%). Crystals suitable for diffraction
were grown by slow evaporation at room temperature of an n-
hexane/CH2Cl2 solution of the complex. Complex 9 (Found: C,
45.10; H, 3.07. C27H22AsCoMoO9 requires C, 45.02; H, 3.08%).
1
2021s, 1980w. NMR (CDCl3), H, δ 7.6–7.3 [m, 20H, Ph]; 13C,
δ 278 [s, µ3-CCl], 202.4 [s, CO], 142.1–128.8 [Ph].
Mass spectrum, m/z 720 (Mϩ) and Mϩ Ϫ nCO (n = 1–4). νmax
/
(ix) Reaction of [Co3(ꢀ3-CMe)(CO)9] and As2Ph4
cmϪ1 (CH2Cl2), 2033m, 2000s, 1971m, 1955 (sh). NMR
(CDCl3), 1H, δ 7.7–7.2 [m, 10H, Ph], 6.41 [s, 1H, AsOH], 5.45 [s,
5H, Cp], 3.48 [s, 6H, Me]; 13C, δ 222.8 [s, MoCo], 205 [s, CoCO],
175.4 [s, CO2Me], 142.8–128.7 [Ph], 90.7 [s, Cp], 72.8 [s,
CCO2Me], 52.7 [s, CO2Me].
[Co3(µ3-CMe)(CO)9] (500 mg, 1.10 mmol) and As2Ph4 (7.3 ml,
0.15 M in toluene, 1.10 mmol) were dissolved in toluene (60 ml)
and heated at 40 ЊC with stirring for 15 h. After removal of the
reaction solvent under vacuum, the residue was dissolved in
the minimum quantity of CH2Cl2 and adsorbed onto silica. The
silica was pumped dry and transferred to the top of a silica
chromatography column. Elution with hexane/CH2Cl2 (9:1)
gave unreacted [Co3(µ3-CMe)(CO)9] (200 mg, 40%), and purple
[Co3(µ3-CMe){µ-(AsPh2)2O}(CO)7] (7b) (210 mg, 22%). Crys-
tals of 7b suitable for diffraction were grown by slow evapor-
ation at 0 ЊC of an n-hexane/CH2Cl2 solution of the complex.
Complex 7b (Found: C, 45.04; H, 2.55. C33H23As2Co3O8
requires C, 45.34; H, 2.65%). Mass spectrum, m/z 874 (Mϩ) and
(xiii) Crystal structure determinations: data collection, structure
solution and refinement
X-Ray intensity data were collected on a Siemens P4 four-circle
diffractometer for 2b, 5, 7a, 7b and 9 and for 4c and 8a on a
Philips PW1100 four-circle diffractometer. Details of data
collection, refinement and crystal data are listed in Table 4.
Lorentz-polarisation and absorption corrections were applied
to the data of all the compounds.
J. Chem. Soc., Dalton Trans., 2000, 395–405
403

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404
J. Chem. Soc., Dalton Trans., 2000, 395–405

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Lorenz, Chem. Ber., 1976, 109, 3741; (d) E. Röttinger, A. Trenkle,
For two of the compounds, 4c and 8a, the positions of the
metal atoms were deduced from Patterson syntheses and for 2b,
5, 7a, 7b and 9 the positions of the metals and most of the
non-hydrogen atoms were located from direct methods. For 4c
and 8a refinement was based on F,31 and for the remaining
structures 2b, 5, 7a, 7b and 9 refinement was based on F2.32 The
remaining non-hydrogen atoms, in all cases, and the hydroxyl
proton in 9, were revealed from subsequent difference-Fourier
syntheses. In the crystal of 5 there are two independent
molecules, which are virtually identical and equivalent param-
eters in the two molecules were “tied” in the refinement. All the
phenyl rings were constrained to refine as rigid hexagons. With
the exception of the hydroxyl proton in 9, all hydrogen atoms
were placed in calculated positions with displacement param-
eters equal to 1.2 and 1.5 Ueq of the parent carbon atoms for
phenyl and methyl hydrogen atoms, respectively. Semi-empirical
absorption correction using ψ-scans33 were applied to the data
of 2b, 5, 7b and 9, and after initial refinement with isotropic
displacement parameters empirical absorption corrections34
were applied to the data of 7a, 4c and 8. All non-hydrogen
atoms were assigned anisotropic displacement parameters in
the final cycles of full-matrix least-squares refinement.
R. Müller and H. Vahrenkamp, Chem. Ber., 1980, 113, 1280.
4 A. J. M. Caffyn, M. J. Mays, G. A. Solan, D. Braga, P. Sabatino,
G. Conole, M. McPartlin and H. R. Powell, J. Chem. Soc., Dalton
Trans., 1991, 3103.
5 (a) A. Martín, M. J. Mays, P. R. Raithby and G. A. Solan, J. Chem.
Soc., Dalton Trans., 1993, 1431; (b) S. L. Ingham, M. J. Mays, P. R.
Raithby, G. A. Solan, B. V. Sundavadra, G. Conole and M. Kessler,
J. Chem. Soc., Dalton Trans., 1994, 3607.
6 G. A. Acum, M. J. Mays, P. R. Raithby, H. R. Powell and G. A.
Solan, J. Chem. Soc., Dalton Trans., 1997, 3427.
7 P. H. Bird, A. R. Fraser and D. N. Hall, Inorg. Chem., 1977, 16,
1923.
8 H. Beurich and H. Vahrenkamp, Chem. Ber., 1981, 114, 2542.
9 (a) P. A. Dawson, B. H. Robinson and J. Simpson, J. Chem. Soc.,
Dalton Trans., 1979, 1762; (b) K. Hinkelmann, J. Heinze, H. T.
Schacht, J. S. Field and H. Vahrenkamp, J. Am. Chem. Soc., 1989,
111, 5078; (c) B. H. Robinson and W. S. Tham, J. Organomet. Chem.,
1969, 16, 45; (d) T. W. Mathewson, B. H. Robinson and W. S. Tham,
J. Chem. Soc. A, 1971, 1457.
10 G. Sànchez, F. Momblona, G. Carcía, G. López, E. Pinilla and
A. Monge, J. Chem. Soc., Dalton Trans., 1994, 2271.
11 G. Conole, M. Kessler, M. J. Mays, G. E. Pateman and G. A. Solan,
Polyhedron, 1998, 17, 2993.
12 W. R. Cullen and J. Trotter, Can. J. Chem., 1963, 41, 2983.
13 P. W. Sutton and L. F. Dahl, J. Am. Chem. Soc., 1967, 89, 261.
14 M. Pizzey, L. Mihichuck, R. J. Barton and B. E. Robertson, Can.
J. Chem., 1984, 62, 285.
CCDC reference number 186/1755.
See http://www.rsc.org/suppdata/dt/a9/a906611j/ for crystal-
lographic files in .cif format.
15 H. Vahrenkamp, Chem. Ber., 1972, 105, 3574.
16 W. Ehrl and H. Vahrenkamp, Chem. Ber., 1973, 106, 2556.
17 A. J. M. Caffyn, M. J. Mays, G. Conole, M. McPartlin and H. R.
Powell, J. Organomet. Chem., 1992, 436, 83.
Acknowledgements
18 B. J. Aylett, Organometallic Compounds, School of Polymer Tech-
nology.2, Wiley, New York, 4th edn., 1979, vol. 1, pp. 413 and 424.
19 C. W. Porter and P. Borgstrom, J. Am. Chem. Soc., 1919, 41, 2048.
20 W. Steinkopf and G. Schwen, Chem. Ber., 1921, 54, 1437.
21 A.-J. Di Maio and A. L. Rheingold, Chem. Rev., 1990, 90, 169.
22 (a) H. W. Sternberg, R. A. Greenfield, J. H. Wotiz, R. A. Friedel,
R. Markby and I. Wender, J. Am. Chem. Soc., 1954, 76, 1457; (b)
R. A. Greenfield, H. W. Sternberg, R. A. Friedel, J. H. Wotiz,
R. Markby and I. Wender, J. Am. Chem. Soc., 1956, 78, 120; (c)
U. Kruerke and W. Hübel, Chem. Ber., 1961, 94, 2829.
23 (a) D. Seyferth, J. E. Hallgren and P. L. K. Hung, J. Organomet.
Chem., 1973, 50, 265; (b) Organometallic Syntheses, ed. J. J. Eisch
and R. B. King, Academic Press Inc., London, 1965, vol. 1.
24 R. Yanez, N. Lugan and R. Mathieu, Organometallics, 1990, 9,
2998.
25 V. Auger, C.R. Hebd. Seances Acad. Sci., 1906, 142, 1151.
26 F. Sachs and H. Kantoriwicz, Chem. Ber., 1908, 41, 2767.
27 F. F. Blicke and F. D. Smith, J. Am. Chem. Soc., 1929, 51, 1558.
28 A. E. Goddard, Textbook of Inorganic Chemistry, ed. J. Newton
Friend, Charles Griffin and Co. Ltd., London, 1930, vol. XI, pt. II,
p. 113.
29 D. Wittenberg and H. Gilman, J. Org. Chem., 1958, 23, 1063.
30 J. Chatt and D. A. Thornton, J. Chem. Soc., 1964, 1005.
31 G. M. Sheldrick, SHELX 76, Program for Crystal Structure Deter-
mination, University of Cambridge, 1976.
32 SHELTXL (PC version 5.03), Siemens Analytical Instruments Inc.,
Madison, WI, 1994.
33 A. C. T. North, D. C. Philips and F. S. Matthews, Acta Crystallogr.,
Sect. A, 1968, 24, 351.
34 N. Walker and D. Stuart, Acta Crystallogr., Sect. A, 1983, 39, 158.
We thank the Defence Evaluation and Research Agency (Fort
Halstead) for financial support to J. D. K.
References
1 (a) R. G. Hayter, J. Am. Chem. Soc., 1963, 85, 3120; (b) R. G.
Hayter, Inorg. Chem., 1963, 2, 1031; (c) R. G. Hayter, J. Am. Chem.
Soc., 1964, 86, 823; (d) R. G. Hayter, Inorg. Chem., 1964, 3, 711; (e)
R. G. Hayter and L. F. Williams, Inorg. Chem., 1964, 3, 717; ( f )
R. G. Hayter and L. F. Williams, J. Inorg. Nucl. Chem., 1964, 26,
1977; (g) J. Chatt and D. A. Thornton, J. Chem. Soc., 1964, 1005; (h)
J. Chatt and D. T. Thompson, J. Chem. Soc., 1964, 2713; (i) J. Grobe,
Z. Anorg. Allg. Chem., 1964, 331, 63; (j) R. G. Hayter, Preparative
Inorganic Reactions, ed. W. L. Jolly, Wiley, New York, 1965, vol. 2,
p. 211; (k) W. Hieber and R. Kummer, Z. Naturforsch., Teil B, 1965,
20, 271; (l) B. E. Job, R. A. N. McLean and D. T. Thompson, Chem.
Commun., 1966, 895; (m) J. P. Candlin, K. K. Joshi and D. T.
Thompson, Chem. Ind. (London), 1966, 1960; (n) W. Hieber and
R. Kummer, Chem. Ber., 1967, 100, 148; (o) W. Hieber and
W. Opavsky, Chem. Ber., 1968, 101, 2996; ( p) M. Cooke, M. Green
and D. Kirkpatrick, J. Chem. Soc. A, 1968, 1507.
2 (a) R. C. Dobbie, M. J. Hopkinson and D. Whittaker, J. Chem. Soc.,
Dalton Trans., 1972, 1030; (b) H. Vahrenkamp, Chem. Ber., 1978,
111, 3472; (c) A. B. Burg and W. Mahler, J. Am. Chem. Soc., 1958,
80, 2334; (d) M. Brockhais, F. Staudacher and H. Vahrenkamp,
Chem. Ber., 1072, 105, 3176; (e) A. Trenkle and H. Vahrenkamp,
Chem. Ber., 1981, 114, 1343; ( f ) J. Grobe, M. Köhne-Wächter and
D. Le Van, J. Organomet. Chem., 1985, 280, 331.
3 (a) F. A. Cotton and T. R. Webb, Inorg. Chim. Acta, 1974, 10, 127;
R. Borowski, D. Rehder and K. J. von Deuten, J. Organomet. Chem.,
1981, 220, 45; (b) H. Vahrenkamp and W. Ehrl, Angew. Chem., Int.
Ed. Engl., 1971, 10, 513; (c) G. Huttner, H.-G. Schmid and H.
Paper a906611j
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